The present invention relates to a material for a container suitable for beverage such as pop drink, coffee, tea and fruit drink and so on, particularly to a steel sheet coated with a resin layer suitable for a thinned, deep drawn and ironed can and a steel sheet therefor.
As a conventional method for forming a container such as a side-seamless beverage can, there is a DI (Drawn and Ironed) can forming method in which organic coating agent is coated on inner and outer surfaces of a formed can.
Further, there is a complex forming method (deep drawing and ironing method) which is a combination of a DTR (Draw Thinning Redraw) method in which a resin film is previously coated on a metal sheet as smooth forming agent and a metal sheet used as a side wall of a can is thinned only by drawing and the DI method (for example, Japanese Patent Publication NO. HEI 6-312223).
In accordance with these methods, a thickness of a sidewall of a can can be thinned and a total weight of a beverage can can be lightened.
The total weight per one can is still expected to become lighter. To accomplish the above purpose, it has been required to thin a thickness of a steel sheet used for a can (thin gauging).
Therefor, new forming methods have been experimented in addition to the conventional forming methods. For example, there is a modification type of the DI forming method with a previous drawing process and a method of which a thickness reduction ratio is much larger than that of a conventional method.
As described above, a thickness reduction ratios of these new methods are much larger than those of a conventional methods. However baneful influence caused by inclusion existed near a surface of a steel sheet becomes serious although such an influence could be ignored in the conventional method. While a can is formed, inclusion are exposed on the surface of the steel sheet and make damage a resin layer coated on the steel sheet. As the result, the inclusions make baneful influence a substrate of the steel sheet in a view of the corrosion resistance.
Thus, a purpose of the present invention is to provide a steel sheet coated with a resin layer wherein a content ratio of respective inclusion is restricted in a steel sheet and the steel sheet is suitable for a can formed by the DI method with excellent the corrosion resistance and a steel sheet therefore.
A steel sheet used for a resin coated steel sheet suitable as a thinned, deep drawn and ironed can recited in claim 1 of the present invention is characterized of comprising Carbon in the range of 0.008% to 0.08%, Silicon of equal or less than 0.05%, Manganese of equal or less than 0.9%, Phosphorous of equal or less than 0.04%, Sulfur of equal or less than 0.04%, Aluminum of equal or less than 0.03%, Nitrogen of equal or less than 0.0035%, residual iron and unavoidable impurities, wherein the steel sheet is characterized in that an average diameter of crystal grains of the steel sheet before covered with a resin layer is equal or less than 8 xcexcm, an average surface roughness (Ra) is equal or less than 0.5 xcexcm and the maximum surface roughness (Rmax) is equal or less than 5 xcexcm.
A steel sheet used for a resin coated steel sheet suitable as a thinned, deep drawn and ironed can as claimed in claim 2 of the present invention is characterized of comprising Carbon in the range of 0.008% to 0.08%, Silicon of equal or less than 0.05%, Manganese of equal or less than 0.9%, Phosphorous of equal or less than 0.04%, Sulfur of equal or less than 0.04%, Aluminum of equal or less than 0.03%, Nitrogen of equal or less than 0.0035%, Boron in the range of 0.0005% to 0.005%, residual iron and unavoidable impurities, wherein the steel sheet is characterized in that an average diameter of crystal grains of the steel sheet before covered with a resin layer is equal or less than 8 xcexcm, an average surface roughness (Ra) is equal or less than 0.5 xcexcm and the maximum surface roughness (Rmax) is equal or less than 5 xcexcm.
A resin coated steel sheet as claimed in claim 3 of the present invention is characterized in that at least one surface of the steel sheet is covered with a resin layer and the resin coated steel sheet is suitable for a thinned, deep-drawn and ironed can.